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XEROX DOCUPRINT NPS GUIDE TO USING PAGE DESCRIPTION LANGUAGES 2-1
2. 2PostScript
This chapter provides an overview of standard PostScript operations
and guidelines for ensuring consistent printer output.
Implementation-dependent operations
The following operations are implementation-dependent.
Floating-point arithmetic and math operators
All PostScript floating-point arithmetic and math operators are
implementation-dependent if you use very large or very small
floating-point numbers. This is rarely a problem with PostScript
masters generated by “real world” creators; that is, commercial
PostScript creators such as Word or Excel. Handwritten test masters,
however, can cause problems.
Some handwritten test masters print out the limits of floating point
numbers and various floating-point operations. Because these
values may vary based on the PostScript implementation, the test
master output also varies, making these tests useless for testing
consistency across different PostScript printers.
Coordinate system default matrix
The PostScript current transformation matrix (CTM) controls the
mapping of user coordinates to device coordinates. You can describe
pages in your own coordinate system and let the PostScript software
transform your requests into the device space. PostScript masters
are device independent only when they do not use the actual CTM
values. When a master needs CTM values, it becomes device-
dependent. The occasional need for CTM values causes inconsistent
output across different PostScript printers.
Some handwritten test masters print out CTM values. Since these
values vary, depending on the device resolution and positioning, the
test master output also varies, making these tests useless for
consistency testing across different PostScript printers.